Design and optimization of uplink multi-user time-reversal DSSS systems

Abstract

Time reversal (TR) filtering can enhance signal strength and reduce interference by exploring multipath transmission in wireless channels. In this paper, for uplink multi-user direct sequence spread spectrum (DSSS) communication systems, a multi-user detection performance enhancement scheme is designed using TR receive filtering and successive interference cancellation (SIC). Under the constraints of the minimum rate requirement and the maximum transmit power of each user, the TR filters and the transmit power of each user are jointly optimized to minimize the total system power consumption or to maximize the sum capacity of the system. In the optimization, the imperfect SIC is considered. The two optimization problems with different objectives are both non-convex. Each original problem is transformed into two optimization sub-problems about the TR filters and the transmit power of each user. The optimal impulse responses (IRs) of the TR filters are obtained by finding the eigenvector corresponding to the maximum eigenvalue of the equivalent channel matrix beam. The transmit power of each user is determined one by one according to the minimum rate requirement when the optimization is to minimize the transmit power, and is obtained by solving the transmit power optimization sub-problem with successive convex approximation when the optimization is to maximize the sum capacity. Simulation results show that the system performance can be effectively improved by using TR filters and SIC, and can be further promoted by jointly optimizing the TR filters and each user’s transmit power.